Temperature detector



Dec. 24, 1968 I HISAO FUTAKI 3,418,648

TEMPERATURE DETECTOR Filed March 9, 1967 if 6 Sheets-Sheet 1 FIG. I

ELECTRIC AL RESISTANCE 40 so 80 I00 I20 140C TEMPERATURE 3 OPERATED -@O-DEVICE. O

3 OPERATED E DEVICE INVENTOR m'sno FuTmu Dec. 24, 1968 I HISAO FUTAKI3,418,648

TEMPERATURE DETECTOR Filed March 9, 1967 6 Sheets-Sheet 3 FIG. 5

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' TEMPERATURE DETECTOR I Filed March 9, 1967' 6 Sheets-Sheet F.

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United States Patent 3,418,648 TEMPERATURE DETECTOR Hisao Futaki,Musashino-shi, Tokyo-to, Japan, assignor to Kabushiki Kaisha HitachiSeisakusho, Tokyo-to, Japan, a joint-stock company of JapanContinuation-impart of application Ser. No. 355,250, Mar. 27, 1964. Thisapplication Mar. 9, 1967, Ser. No. 621,848 17 Claims. (Cl. 340-228)ABSTRACT OF THE DISCLOSURE Temperature detector using as its sensor acritical temperature resistor fabricated by oxide semiconductorcomprising fine grains of V0 (or V 0 crystal. The resistor has a lowresistance-temperature coefficient within a range below a certaindefinite temperature and an extremely large negativeresistance-temperature coefiicient to appear when the temperatureexceeds the abovementioned definite temperature. A highly stable andsensitive detector is obtainable by using such critical temperatureresistor as its sensor, for the definite temperature is equal to or nearthe desired detecting temperature or set operation temperature.

This application is a continuation-in-part of a prior application U.S.Ser. No. 355,250 filed Mar. 27, 1964, in the name of Hisao Futaki,entitled Temperature Detector, and now abandoned.

This invention relates to a temperature detecting device and moreparticularly to a new temperature detector having desirablecharacteristics, in which a unique oxide semiconductor is used.

In my application Ser. No. 484,510, filed Aug. 24, 1965 and nowabandoned, as a continuation-in-part of my earlier application Ser. No.266,235, filed Mar. 19, 1963 and now abandoned, a unique resistor hasbeen disclosed. The resistor possesses an extremely large negativeresistancetemperature coefficient within a given specific range and asmall resistance temperature coefficient just below and above saidrange, the resistance value of which decreases abrupt'y and stepwisewith a temperature increase in excess of the upper limit of thetemperature range, wherein an extremely large resistance-temperaturecoetlicient prevails (i.e. while the temperature rises by about C., itsresistance value decreases by about Such resistor will hereinafter bereferred to by the tentative nomenclature as a critical temperatureresistor.

This critical temperature resistor is composed of an oxide semiconductorwhich is obtained by reduction of mixtures of vanadium pentoxide andother oxides in a reducing atmosphere and of simultaneous or subsequentsintering of the reduced oxide mixes. For the abovementioned otheroxides, oxides of phosphorus (P), silver (Ag), lithium (Li), sodium(Na), potassium (K), beryllium (Be), magnesium (Mg), calcium (Ca),lanthanum (La), cerium (Ce), zirconium (Zr), zinc (Zn), cadmium (Cd),boron (B), aluminum (Al), silicon (Si), tin (Sn), bismuth (Bi), uranium(U), and yttrium (Y) can be used singly or in mixture. When theabovementioned oxide semiconductor is observed through an electronmicroscope, it is seen that fine crystals of V0 (or V 0 deposited in thecourse of the abovementioned reduction and sinter-treatment scatter inthe sintered body of the mixture of vanadium pentoxide (V 0 and otheroxides in a state of being surrounded by them. The abrupt change in theresistance value of this critical temperature resistor is caused by thefine crystals of V0 and, in order to obtain a favorabletemperature-resistance characteristics,

See

the fine crystals of V0 may preferably be contained to more than 5 molpercent in the above mentioned oxide semiconductor. In case the V0content is less than 5 mol percent, the degree of variation in theresistance value becomes small. Consequently, in the abovementionedreduction-treatment, it is necessary to continue reduction until suchtime that said vanadium pentoxide is converted to a sufficient quanty ofV 0 It should also be taken care that when the fine crystal of theabovementioned V0 is too large in size, a hysteresis phenomenon (aphenomenon wherein the locus of variation in the resistance value whenthe temperature is gradually increased and that when the temperature iscaused to decrease do not coincide) would inevitably appear in thetemperature-resistance characteristics, and, moreover, thecharacteristics will become gradually deteriorated as the criticaltemperature resistor is used repeatedly. In this sense, the V0 crystalshould be controlled to as small a size as possible, or, preferably lessthan a few tens of microns. In order to obtain such fine crystal in theaforementioned manner, the best way contemplated is to abruptly cool theoxide semiconductor while it is being kept heated after sintering.

During the process of reduction or sintering, vanadium pentoxide V 0 andthe aforementioned other oxides to be mixed with V 0 are melted by heat,and fine crystals of V0 are deposited out of the melt of the mixture.The heating temperature at this time should be lower than the meltingpoint of V0 (or V 0 After the cooling, the mixture is to surround thefine crystals of V0 further connects the crystals mutually andelectrically and, at the same time, functions to prevent the electricalcharacteristics of V0 from being varied with lapse of time underinfluence of external atmosphere. It has heretofore been known that asingle crystal of V0 undergoes abrupt change in its resistance valuewithin a certain specific temperature range, the same as a thermistorhaving the aforementioned composition. However, this element consistingof single crystal of V0 is disadvantageous in that deterioration in itselectrical characteristics with lapse of time is enormous becausevanadium dioxide directly contacts air to change its characteristicsand, moreover, the size of the crystals is large with the consequentemergence of hysteresis phenomena. On account of these facts, V0monocrystal has not become practically useful.

The temperature range, in which the resistance value of theabovementioned oxide semiconductor varies abruptly is from C. to 75 C.,and the principal range of the abrupt change is between C. and C.,theoretically, this abrupt change takes place at 67.5 C. An oxidesemiconductor containing as its principal constituent vanadium oxidewhose temperature range for its abrupt change is lower than 60 C. orhigher than C. has been disclosed in my copending application Ser. No.475,- 129, filed July 27, 1965. According to this application, at leastone of the elements such as germanium (Ge), iron (Fe), cobalt (Co),nickel (Ni), manganese (Mn), titanium (Ti), niobium (Nb), tungsten (W),molybdenum (Md), tantalum (Ta), and chromium (Cr) is disposed orintroduced in the state of solid solution in the fine crystals of V0This latter oxide semiconductor is obtained by first mixing theaforementioned other oxides or the oxides of the abovementioned elementsin place thereof with vanadium pentoxide (V 0 heat-treating this mixturein a reducing atmosphere at a temperature which is higher than themelting (or softening) point of the mixture, but is lower than themelting point Of the V0 crystals, and depositing fine crystals of V0from the melt of this mixture of V 0 and the abovementioned oxides. Asmall quantity of the abovementioned metal element is dispersed orintroduced in the fine crystals of V0 In case Ti and/or Ge are containedin the V fine crystals, the temperature range within which theresistance value changes abruptly becomes higher than that when theseelements are not present. On the other hand, when Fe, Co, Ni, Mn, Nb, W,Md, Cr and/or Ta is contained in the V0 fine crystals, theabovementioned temperature range becomes lower than that in the case oftheir being not present. As stated in the foregoing, the criticaltemperature thermistor containing the abovementioned fine crystals of V0possesses a characteristic such that its resistance value decreasesabruptly with increase in temperature within a certain definitetemperature range. This thermistor further indicates peculiar change inthe current-voltage characteristics which can not be seen in theconventional thermistor. That is, when the ambient temperature is keptconstant, the degree of variation in voltage appearing across theterminals of the thermistor with respect to variation in current flowingin the thermistor becomes remarkably large, and the abovementionedvoltage value attains its maximum at a certain specific current value.The maximum value of this voltage decreases with increase in the ambienttemperature, in which case the rate of decrease in the maximum voltagevalue with respect to variation in the ambient temperature is great;particularly, the value is subjected to remarkable variation withrespect to variation in the ambient temperature corresponding to thetemperature range within which the abovementioned resistance valuechanges abruptly. Such electrical characteristics could not be expectedfrom the conventional thermistor, wherein the resistance value changesonly exponentially with respect to temperature variation.

The present invention intends to apply the abovementioned criticaltemperature thermistor as a sensor for temperature detector in utilizingthe characteristics the thermistor possesses such that (1) it hasextremely large negative resistance-temperature coefiicient with aspecific temperature range and, in the course of this range, theresistance value thereof abruptly decreases with rise in temperature;(2) it has extremely small resistance-temperature coefi'lcient at normaltemperature or at a temperature lower than the abovementionedtemperature range, hence variation in resistance value with respect tovariation in temperature is extremely small at that specifictemperature; (3) it has large variation in the maximum voltage valuewith respect to temperature, the variation being particularly remarkablewith respect to variation in the ambient temperature corresponding tothe abovementioned specific temperature range, and so forth. By thepresent invention, it has become possible to obtain the temperaturedetector whose operation is stable, accurate and highly sensitive.Furthermore, the detecting device of the present invention can providehighly reliable contactless switching operation. These unique featurescannot be expected from the known type of temperature detecting devices.

It is therefore the principal object of the present invention to providea temperature detecting device having extremely accurate operation, lessmalfunction, and extremely high sensitivity with respect to finevariation in temperature.

The specific nature, principle, and details of the invention will bemore clearly apparent by reference to the following description, takenin conjunction with the accompanying drawings in which;

FIG. 1 is a graphical representation indicating the relationship betweentemperature and electrical resistance of a critical temperatureresistor;

FIG. 2 is a graphical representation indicating currentvoltagecharacteristics of a critical temperature resistor;

FIG. 3 is a circuit diagram indicating the principle of the invention;

FIG. 4 is a circuit diagram showing a preferred embodiment of thetemperature detector according to the invention;

FIG. 5 is a graphical representation indicating the relationship betweentemperature and electrical resistance of other critical temperatureresistors; and

FLIGS. 6, 7 and 8 are graphical representations indicatingcurrent-voltage characteristics of other critical temperature resistors.

Referring to FIG. 1 which shows one example of resistance-temperaturecharacteristics of a critical temperature resistor which has thecomposition of material: V of 7.1 parts, P of 1.1 parts, and Sr of 1.8parts in gramatoms (the composition may be indicated as V 7.1, P 1.1, Sr1.8), or V 0 of 60 mol percent, P 0 of 10 mol percent and SrO of 30 molpercent, it is seen that the resistance value of the resistor abruptlydecreases by from 15 kilo-ohm to 5 ohm within the temperature range of6070 C. and that the variation in the resistance value in response tothe temperature variation is small below 60 C. and above 70 C.

Referring to FIG. 2, which shows one example of current-voltagecharacteristic curves of said critical temperature resistor, which hasthe composition of V 7.1, P 1.1, Sr 1.8, curves 5, 21, 22, 23, 1 and 3are those respectively corresponding to surrounding temperature T of 20,30, 40, 50, 60, 65 degrees C.

These curves have a point at which the voltage attains a maximum, andthe voltage peak values in curves 5, 1 and 3, respectively are shown asE E and E The variation in this voltage peak value in response to thetemperature variation is larger in comparison with that in theconventional thermistors. FIG. 2 shows the voltage peak values at theambient temperatures T of 20 C., 30 C., 40 C., 50 C., 60 C. and 65 C. as30 v., 24 v., 19 v., 13 v., 2.5 v. and 0.5 v., respectively. Inparticular, it can be clearly seen from the drawing that the voltagepeak r value considerably decreases at a temperature of about 60 C.Namely, while the gap of the voltage peak values between T =20 C. and T:30 C. is about 6 v., the gap of the voltage peak values between T,,=50C. and T =60 C. is about 10.5 v. In this invention, the voltage peak atthe ambient temperature of 60 C. is an important point for detecting theambient temperatures of 60 C.

When a resistance as indicated by 7 in FIG. 2 having a resistance valueof ohms is connected in series with the critical temperature resistor atthese different temperature conditions, curves 6, 2 and 4 of FIG. 2 areobtained.

The circuit shown in FIG. 3, indicating the principle of the temperaturedetector of the invention, consists of a series-connection of a criticaltemperature resistor 1, a series resistor 2, a device 3 such as an alarmor indicator, and a power source 4. The critical temperature resistor 1is installed in an exposed state at a point where the surroundingtemperature is to be detected so that resistance value will varysensitively in response to the temperature andhas a miniature size sothat its time constant will be small. The components of the circuitother than the critical temperature resistor 1 may be installed at apoint other than that where the temperature is to be detected.

The principle of operation of the circuit shown in FIG. 3 will now beconsidered. First, at the normal ambient temperature, a voltage which islower than the voltage peak value E of the current-voltagecharacteristic curve of the critical temperature resistor 1 is impressedon the said resistor 1.

When, for example, a critical temperature resistor 1 havingcharacteristics as shown in FIG. 2 is used at an ambient temperature Tof 20 C., the voltage peak value E will be E =30 v. Therefore, the powersource 4 is selected in such a manner that the voltage E to be impressedon resistor 1 becomes less than 30 v. at E When it is intended tooperate the detector at the ambient temperature of, for example, 60 C.,the power source 4 is selected in such a manner that the voltage E to beimpressed on said resistor 1 at T of 60 C. is equal to E (about 2.5 v.),since it is apparent from FIG. 2 that the voltage peak value E at T =60C. is 2.5 v.,

At the normal ambient temperature (e.g. T =20 C.), since the voltagepeak value E is higher than the voltage E impressed on said criticaltemperature resistor 1 (the voltage E is nearly equal to said voltage Ethe current thereby flowing in said resistor 1 is stabilized by beingsuppressed with a smaller value than that of the current I In case thetemperature of the resistor 1 is lower than 60 C., the resistance valueof the critical temperature resistor 1 becomes more than kilo ohms asshown in FIG. 1 which is far greater than the resistance value of 100ohms obtained by summation of the internal resistances of theseries-resistance 2 and the operated device 3 with the consequence that,in case of the ambient temperature being less than 60 C., the currentflowing through the temperature detector is actually determined by theresistance value of the resistor 1. Accordingly, the required voltagevalue E of the power source will be substantially equal to theabovementioned voltage E (e.g. about 2.5 v. as shown in FIG. 2). (Thevoltage value B is usually selected higher than the value of E, for thevoltage decrease due to the resistance 100 ohms.)

As the surrounding temperature gradually rises, the resistance of thecritical temperature resistor 1 decreases in response to thissurrounding temperature, and in the current-voltage characteristicrepresentation, the voltage peak value E gradually becomes lower. When,at or over the ambient temperature T of 60 C., the voltage peak value Ebecomes equal to or lower than E or E it immediately shifts to thestabilizing point 8 (the point being indicated by E in I in FIG. 2) withthe consequence that a large current flows suddenly in the criticaltemperature resistor, assuming a value such as an 1 The device 3, suchas alarm or indicator, is thereby operated by this large current. Thedevice 3 can be simply a means to detect variations in current flowingin this circuit, in which case a signal corresponding to variation ofcurrent which has been emitted and detected is transmitted to otherdevice.

In this example, as the maximum (or peak) voltage value widely varieswith respect to slight variation in temperature in the vicinity of T :60C., the currentvoltage to be impressed on the resistor at T =20 C. neednot be adjusted exactly at 2.5 v. For example, even when a voltagehaving a range of 1.5 v.3.5 v. is applied, the temperature to be finallydetected will be 60:1 C., hence it is possible to detect with extremeaccuracy the temperature of 60 C. which is primarily intended.Accordingly, the instant detector does not operate erroneously withvariation to some extent in the applying voltage value of the voltagesource, whereby it is possible to detect with high sensitivity andaccuracy the intended definite temperature.

In the foregoing example, explanation has been made with respect to acase wherein the total resistance obtained by adding the internalresistances of the series-resistance 2 and the operated device 3 is 100ohms as shown by curve 7 in FIG. 2). In case it is desired to obtainlarger set operating current I this total resistance can only be reducedwithin an allowable range of power loss due to the resistance 1. Furtherit is to be noted that the abovementioned series-resistance 2 is notalways necessary, but it can be dispensed with when the internalresistance of the operated device is sufiiciently large. In other words,desired operating current can be obtained by controlling the value ofthe resistance 2 alone. The temperature at which the instant temperaturedetector is intended to be operated can be adjusted by appropriateselection of the voltage E of the power source 4. In case the operateddevice 3 is actuated by current, it is desirable to utilize a constantvoltage source as the power source 4.

In one embodiment of the temperature detector according to the inventionas shown in FIG. 4, critical temperature resistors 1, 1a 1m areconnected in parallel with respect to an operated device 3, such as analarm or an indicator, and a power source 4, connected in series withthe device 3. In addition, pilot lamps 5, 5a 5m are connected in serieswith the critical temperature resistors 1, 1a 1m respectively, and serveto indicate clearly which of the critical temperature resistorsdistributively installed for temperature detection is operating, and atthe same time, serve to verify temperature detection in a simple manner.These pilot lamps 5, 5a 5m respectively correspond to the resistor 2 inFIG. 3.

When the conventional thermistor in which the resistance value variesalmost exponentially with variation in temperature is utilized, it hasbeen sufficient to use the one having large resistance-temperaturecoefficient for the purpose of constructing a detector having highsensitivity with respect to variation in temperature. However, in viewof the fact that the resistance-temperature coefiicient thereof at thenormal temperature is as large as that in the vicinity of the operatingtemperature, there has been apprehension such that the device wouldcommence operation before it attains the set operating temperature,hence the operation of the device is unstable. The temperature detectorof the present invention is completely free from such disadvantage.

Other examples of the present invention will be ex plained hereinbelowwith reference to FIGS. 5 through 8 inclusive. In FIG. 5, the curves 9,10, and 11 respectively indicate the temperature-resistancecharacteristics of the critical temperature resistor whose materialcomposition is respectively V 6-P 2-Fe 2, V 8.5-P 1.0-Mo 0.5, and V 8-Srl-G 1. In this graphical representation, the abscissa is temperature C.)indication which is graduated by natural number scale, and the ordinateis electrical resistance (ohm) indication which is graduated bylogarithmic scale. The same graduation is applicable to FIGS. 6, '7, and8.) As seen from this graph, the critical temperature resistor shown interms of the characteristics curves 9, 10, and 11 possesses, unlike thatas shown in FIG. 1, regions wherein the resistance value thereofabruptly decreases within the respective temperature ranges of 50-60 C.,3545 C., and 7090 C.

The current-voltage characteristics of the critical temperature resistorhaving the composition of V 6-P 2-Fe 2 is shown in FIG. 6, from which itis seen that the curves 12, 13, and 14 respectively correspond to thoseat the ambient temperature of T =25 C., T =50" C., and T =60 C. Thecircuit constructed with this critical temperature resistor will now beexplained hereinbelow with reference to FIG. 3. In this example, thevoltage value E of the power source 4 is so selected that the voltage Eto be impressed on the resistor 1 will become equal to E when theambient temperature T reaches 50 C. on the ground that the resistancevalue of this resistor abruptly decreases at the temperature range of50-60 C. From FIG. 6, the value of E is found to be 12 volts or so, thevoltage value E is so selected as to be equal to E =l2 v. (Actually, thevalue E is chosen slightly higher than the value of E As for theresistance value, the resistor 2 and/or operated device 3 are soselected that the composite resistance of the internal resistance of theresistor 2 and the operate-d device 3 (more strictly, the compositeresistance includes the internal resistance of the power source 4, too)becomes equal to, for instance, ohms. In this way, a device fordetecting that the ambient temperature of the resistor 1 has reached 50C. can be obtained. In this device, when the ambient temperature of theresistor reaches or exceeds that specific temperature of 50 C., theoperated device 3 commences operation.

FIG. 7 indicates the current-voltage characteristics of the criticaltemperature resistor having the material composition of V 8.5-P 1.0-Mo0.5, wherein the curves 15, 16 and 117 respectively correspond to thoseat the ambient temperature of T =0 C., T.,,=35 C., and T =60 C. Inconstructing the circuit shown in FIG. 3 by using this criticaltemperature resistor, the power source 4 is so selected that the valueof E becomes equal to E =0-.4 v.

r if and when the specific operating temperature is selected at T,,=35C. Furthermore, the resistance value of the resistance to be seriallyconnected with the resistor 1 is selected at, for example, 4-10 ohms. Inthis case, the resistor 2 will probably be unnecessary and it issufiicient to select an element having small internal resistance as theoperated device 3.

FIG. 8 shows the current-voltage characteristics of the criticaltemperature resistor having the material composition of V 8-Sr l-Ge 1,wherein the curves 18, 19, and 20 respectively correspond to those atthe ambient temperature of T =25 C., T, =70 C., and T,,-=90 C. When thiscritical temperature resistor is used for constructing the circuit shownin FIG. 3, the power source 4 is so selected that the value of E becomesequal to 0.9 v. since the value of E is 0.9 v. as seen from FIG. 8, andthe resistance value to be serially connected with the resistor 1 isselected at, for example, 1001O ohms. Thus, when the ambient temperatureof the resistor 1 reaches or exceeds the temperature limit of 70 C., theoperated device 3 commences operation to detect variation intemperature.

It should be understood, of course, that the foregoing disclosurerelates to only a preferred embodiment of the invention and that it isintended to cover all changes and modifications of the example of theinvention herein chosen for the purposes of the disclosure, which do notconstitute departures from the spirit and scope of the invention as setforth in the appended claim.

What I claim is:

1. A temperature detector for detecting rise in temperature above adefinite temperature at least one point in space comprising at least onesensor composed of a critical temperature resistor containing oxidesemiconductor which consists of sintered oxide member and fine grains ofvanadium dioxide V0 crystal scattered in and surrounded by said oxidemember, and which has, in the current-voltage characteristics thereof, apoint at which the voltage attains a maximum value, said maximum voltagevalue decreasing as the ambient temperature rises; a power source meansto apply to said critical temperature resistor in an ambient temperaturelower than said definite temperature a voltage equal to or near themaximum voltage value which the critical temperature resistor has insaid ambient temperature equal to said definite temperature; and meansto detect abrupt increase in current flowing in of said criticaltemperature resistor when the ambient temperature of said sensor risesto a value not lower than said definite temperature.

2. The temperature detector according to claim 1, wherein said sinteredoxide member comprises at least one oxide selected from the groupconsisting of oxides of phosphorus, silver, lithium, sodium, potassium,beryllium, magnesium, calcium, lanthanum, cerium, zirconium, zinc,cadmium, boron, aluminum, silicon, tin, bismuth, uranium and yttrium.

3. The temperature detector according to claim 1, wherein the amount ofsaid vanadium dioxide V0 crystals contained in said sintered oxidemember is at least 5 mol percent of said oxide semiconductor.

4. The temperature detector according to claim 1, wherein said finegrains of vanadium dioxide V0 crystal contain at least one kind ofelement selected from the group consisting of germanium, iron, cobalt,nickel, manganese, titanium, niobium, tungsten, molybdenum, tantalum andchromium.

5. The temperature detector according to claim 1, further comprisingresistor means connected in series with said sensor.

6. The temperature detector according to claim 5, wherein said criticaltemperature resistor possesses an extremely large negativeresistance-temperature coefficient within a specific temperature rangejust above said definite temperature and a small negativeresistance-temperature coetficient just below said temperature range,

and the resistance value of said serially connected resistor means is sodetermined that the total resistance value of the internal resistance ofsaid power source means, the internal resistance of said detectingmeans, and a resistance value to be serially connected with saidcritical temperature resistor including the resistance of said resistorbe smaller than the resistance value of said critical temperatureresistor at a temperature lower than said temperature range, but largerthan that at a temperature higher than said temperature range.

7. The temperature detector according to claim 1, wherein said powersource means is a constant voltage source, and said detecting means isconnected in series with said critical temperature resistor and powersource and is actuated by abruptly increased current flowing in saidcircuit construction when the ambient temperature of said sensor becomesnot smaller in value than the said definite temperature.

8. The temperature detector according to claim 1, wherein a plurality ofsaid sensors are mutually connected in parallel.

9. The temperature detector according to claim 1, wherein said criticaltemperature resistor has a low resistance-temperature coeflicient withinthe temperature range below said definite temperature, and an extremelylarge negative resistance-temperature coefficient to appear when thetemperature exceeds said definite temperature.

10. A temperature detector for detecting rise in temperature above adefinite temperature at least one point in space comprising at least onesensor composed of a critical temperature resistor containing oxidesemiconductor which consists of sintered oxide member and fine grains ofvanadium dioxide V0 crystal scattered in and surrounded by said oxidemember, which has a low resistance-temperature coefiicient within thetemperature range below said definite temperature and an extremely largenegative resistance-temperature coefficient to appear When thetemperature exceeds said definite temperature, and which has, in thecurrent-voltage characteristics thereof, a point at which the voltageattains a maximum value, said maximum voltage value decreasing as theambient temperature rises; a resistance means; a power source means toapply to said critical temperature resistor in an ambient temperature avoltage equal to or near the maximum voltage value which the criticaltemperature resistor has in an ambient temperature equal to saiddefinite temperature; means operated by the current flowing through saidsensor when the ambient temperature of said sensor rises to a value notlower than said definite temperature; and means to connect in seriessaid sensor, said resistance means, said power source, and said operatedmeans.

11. The temperature detector according to claim 10, wherein said oxidemember comprises an oxide of vanadium and an oxide of at least one metalselected from the group consisting of phosphorus, silver, lithium,sodium, potassium, beryllium, magnesium, calcium, lanthanum, cerium,zirconium, zinc, cadmium, boron, aluminum, silicon, tin, bismuth,uranium and yttrium, the amount of said fine grains of vanadium dioxidecrystal being at least 5 mol percent of said oxide semiconductor, andsaid definite temperature being in the vicinity of 60 C.

12. The temperature detector according to claim 10, wherein said finegrains of vanadium dioxide crystal contain in the state ofsolid-solution a small amount of at least one metal selected from groupconsisting of germanium and titanium, and said definite temperature isabove 60 C.

13. The temperature detector according to claim 10, wherein said finegrains of vanadium dioxide crystal contains in the state ofsolid-solution a small amount of at least one metal selected from thegroup consisting of iron, cobalt, nickel, manganese, niobium, tungsten,

molybdenum, tantalum and chromium, and said definite temperature isbelow 60 C.

14. A temperature detector for detecting an ambient temperature above 60C. comprising: a critical temperature resistor containing V 71%, P 11%,and Sr 18% in gram atomic weight; a voltage source for supplying avoltage of about 2.5 volts to said critical temperature resistor at anambient temperature below 60 C., means for raising the ambienttemperature above 60 C.; and detecting means to detect increase in acurrent flowing in said critical temperature resistor.

15. A temperature detector for detecting an ambient temperatsre above 50C. comprising: a critical temperature resistor containing V 60%, P 20%,and Fe 20% in gram atomic weight; a voltage supplying means forsupplying a voltage of about 12 volts to said cri-tical temperatureresistor at an ambient temperature below 50 C.; means for raising theambient temperature above 50 C.; and detecting means to detect anincrease in a current flowing in said critical temperature resistor.

16. A temperature detector for detecting an ambient temperature 35 C.comprising: a critical temperature resistor containing V 85%, P 10%, andMo in gram atomic weight; a voltage supplying means for supplying avoltage of about 0.4 volt to said critical temperature resistor at anambient temperature below 35 C.;

and detecting means to detect an increase of current flowing in saidcritical temperature resistor.

17. A temperature detector for detecting an ambient temperature above C.comprising: a critical temperature resistor containing V Sr 10%, and Ge10% in gram atomic weight; a voltage supplying means for supplying avoltage of about 0.9 volt to said critical temperature resistor at anambient temperature below 70 C.; means .for raising the ambienttemperature above 70 C.; and detecting means to detect an increase ofcurrent flowing in said critical temperature resistor.

References Cited UNITED STATES PATENTS 2,977,558 3/1961 Hampton e-338-22 3,149,298 9/ 1964 Handelman 338-22 3,199,087 8/1965 Foglia340-173 3,226,600 12/1965 Zielasek 315-209 OTHER REFERENCES IBCtechnical disclosure bulletin, Temperature Detector, A. I. Meyers, vol.4, No. 3, p. 71, August 1961.

JOHN W. CALDWELL, Pimary Examiner.

DONALD J. YUSKO, Assistant Examiner.

